Adam Mann's Wired article outlines the latest discoveries relevant to possible Martian life. If nothing else, this sets the bar for possibly life pretty low: any Martian life produces either produces little methane, is very sparse, or both. Thoughts?

NASA’s Curiosity rover has sniffed the Martian atmosphere for methane and, so far, turned up empty. The much-anticipated measurement strikes a blow to the hope that previous hints of methane could have been an indication of life on Mars.

Methane, made of one carbon and four hydrogen atoms, is one of the simplest organic compounds. On Earth, 90 to 95 percent of methane in the atmosphere comes from biological activity, mainly methanogenic bacteria and cow farts. Geological activity such as water-rock interactions could have also produced the methane, which would also have overturned astronomers’ view that Mars is geologically dead in the modern age. Curiosity’s latest measurements seem to refute both ideas.

“So far we have no definitive detection of methane,” said chemist Chris Webster, instrument lead on Curiosity’s Sample Analysis at Mars (SAM) laser spectrometer, during at NASA press conference today. SAM is like the rover’s “nose,” able to test the Martian atmosphere and determine what chemicals are present.

In 2009, Michael Mumma of NASA’s Goddard Space Flight Center in Greenbelt, Maryland used an Earth-based telescope and found hotspots of methane that appeared seasonally. Methane is quickly destroyed by ultraviolet radiation in the Martian atmosphere, usually after only a few hundred years, so the gas could not be left over from some era millions of years ago. The detection excited much of the scientific community because these hotspots could have been areas where underground Martian microbes were alive on modern-day Mars.

Later measurements by both Mumma and other scientists cast doubt on these methane detections, and one of Curiosity’s main tasks has been to provide evidence one way or another. The probe used its Tunable Laser Spectrometer (TLS) and found the atmosphere is mainly composed of carbon dioxide, with trace amounts of argon, nitrogen, and oxygen.

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